Novel fishway entrance modifications for Pacific lamprey

Technical fishway passage structures provide high passage efficiency and effective passage for adult Pacific salmonids at eight large dams

“…Operational criteria at the CRB fishways include hydraulic head differentials at the openings of ~0.3 m which generate fish attraction plumes with velocities targeted at adult salmonids ranging from ~1.5–3.0 m/s [e.g., 42 , 64 , 97 ]. The highest plume velocities tend to be near the tailrace surface where they are attractive to salmonids and American Shad Alosa sapidissima , but not necessarily for less fusiform native species like White Sturgeon Acipenser transmontanus and Pacific Lamprey Entosphenus tridentatus that also use the CRB fishways [ 97 , 98 , 100 ].…”

“…Researchers and managers should use caution when comparing these types of dam-wide passage metrics to site-specific metrics at the CRB dams or elsewhere. Notably, recent modifications to fishway entrances at some CRB dams, such as the Bonneville Dam Cascades Island fishway entrance, have included installation of ‘keyhole’ weirs with narrow profiles near the surface to increase attraction velocity, and, in conjunction with flow-disruption devices inside the fishway, wide profiles near the bottom of the weir to reduce velocity near the fishway floor for co-migrating non-salmonid species such as Pacific Lamprey [ 42 ]. The modifications reduced maintenance compared to telescoping weirs, provided an increased range of passage conditions for fish, and were demonstrated to maintain or increase passage rates for adult salmonids [ 42 ].…”

“…In the pre-ladder segments, a substantial volume of water was pumped through floor and wall diffusers to maintain hydraulic head at the fishway openings. Consequently, attraction cues could be confusing, particularly in the transition areas, and several studies have described how upstream migrants from multiple species often turn around near the base of CRB fish ladders and move back downstream to the tailrace [e.g., 42 , 82 , 100 ]. In an unpublished analysis using data from several study years, we estimated that ~30–62% of adult salmonids exited to the tailraces at least once at Bonneville and The Dalles dams and ~56–85% exited at least once from the John Day Dam fishways.…”

“…Endangered Species Act protections for many CRB populations [ 36 , 37 ]. Adult salmonid migration research topics have ranged from narrowly-defined questions about how CRB fishway structures or dam operations affect fish behaviors at project-specific spatial scales [e.g., 38 – 42 ], to system-wide evaluations of upstream migration rates [ 43 , 44 ] survival [ 45 , 46 ] and homing success [ 47 , 48 ]. Radiotelemetry has been the primary technological tool in the CRB adult salmonid program, and the large datasets have also been used to investigate broader ecological questions.…”

Global advances in fish passage research and practice

“…The unique case of providing passage for amphidromous species (Jarvis and Closs 2019); Using flume experiments to define fish passage criteria; Considerations for entrance design and location (Moser et al 2019) Providing sustainable outcomes for humans, whist minimising environmental impacts, are a constant challenge for river developers. In some cases it will be impossible for fish passage to address all of the expected impacts of a river development project.…”